Process of bleaching asbestos



UNITED STATES CHESTER L. HILL, .0]? LANCASTER, PENNSYLVANIA.

PROCESS OF BLEACI-IING ASBESTOS.

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No Drawing.

To all whom it may concern:

Be it known that I, CHESTER L. HILL, a citizen of the United States, residing at Lancaster, in the county of Lancaster and State of Pennsylvania, have invented certain new and useful Improvements in Processes of Bleaching Asbestos; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same. a

This invention consists in the novel features hereinafter described, andparticularly pointed out in the following specification and claims. F

The best quality of asbestos obtained from the Dominion of Canada is naturally snow white and very free from foreign matter. The asbestos obtained from other localities, for example some South African asbestos and various grades of asbestos from other localities, is of a dirty brown color, which color is imparted to the fibers largely by the presence in association with them of iron usually in the form of oxid, which in the case of South African brown asbestos is usually in the form of limonite. On account of the growing demand for asbestos products and the difficulty of adequately increasing the output at the mines, the price of the white Canadian asbestos has greatly increased, and it is highlyimportant to utilize the asbestos from other sources to meet the increased demand. It has been'found that the South African and other brown asbestos can be bleached, by treating it with a liquid solution of an acid in water to remove the coloring matter, but in so treating the fibrous asbestos, very large quantities of the bleaching solution must be employed, as it is necessary to thoroughly wet the asbestos in order to remove the coloring matter, and the large quantities of chemicals required for the purpose has madethis process practically prohibitive from the commercial standpoint.

The object of my lnvention is to effect the bleaching of asbestos fiber, and particularly South African asbestos commercially by the I have discovered that this desirable result pecification of Letters Patent.

Application filed May 1, 1920.

Patented July 13, 1920.

Serial No. 378,046.

can be accomplished by treating the asbestos fibers with an acid in the vapor or gaseous stage in association with moisture preferably in the form of steam or water vapor to convert the colored material, principally iron compounds, into soluble salts, which are thereafter washed out with Water. I have found 1n carrying out my improved process that an immense saving of the acid employed is effected, and that the acid acts more powerfully in the gaseous or vapor stage without association with the large quantlties of water required in the liquid treatment, so that the bleaching effect is rendered almost instantaneous, and the entire bleaching operation can be effected in a remarkably short space of time, and with great economy. In carrying out my invention, I prefer to maintain the fibers in open or separated relation, which may be accomplished in any one of a number of ways, as by tumbling the fibers in a rotating drum or tumbler while they are being acted upon by the acid gas and vapor, or the fibers may be held in loose layers or perforated trays or partitions within a stationary container, and I also prefer to maintain the fibers at a sufliciently high temperature to prevent condensation of the acid gas or gas and vapor before it has effected the desired chemical reaction.

In the following specification, l have described the preferred manner in which I have carried my invention into effect. In accordance with my inventionthe asbestos fibers, after being loosened up, and either before or after being washed to free them from the dirt and other foreign matter, as preferred, are charged, practically dry, into a suitable container or closed receptacle, the interior of which is acid proof. For this purpose I may use a receptacle made of stoneware or earthenware, or a metal receptacle lined with enamel, or any other form of receptacle provided with an acid resisting interior surface. It is desirable that the fibers shall not be too denselypacked in the receptacle, and to this endv I may provide for supporting the receptacle upon suitable trunnions upon which it can be rotated during t-he bleaching process, after the manner of the well known tumblers, or I may provide the container, if

it is stationarily supported, with a, plurality from the other portions of the fibers in the container, to prevent them from becoming too tightly packed. I may employ one or a series of these containers, and T prefer in fact to employ a plurality of containers which are connected to each other in series.

For the bleaching agent I prefer to em ploy commercial hydrochloric acid, which upon heating and distillation readily forms a constant boiling mixture ofwater and hydrochloric acid gas. That is to say, the vapor driven off from hydrochloric acid by the application of sufficient heat to vaporize it, will contain a substantially constant percentage of the gas throughout the vaporization of the hydrochloric acid. The hydrochloric acid is heated in any desired way to the boilingpoint and the vapor which thereforecomprlses water vapor and hydrochloric acid gas 1n intimate association is led into .the container containing the asbestos" fibers to be bleached and is passed therethrough,

' and where a series of these containers is employed, the vapor is led through all of them in series passing from one to the other and through and into intimate association with the asbestos fibers in each container. If the containers are rotatable, the vapor will be led into and conducted from the same through the trunnions in a well known way, so as not to interfere with the rotation of the container.

Each container is preferably provided with heating means for maintaining the interior at such a temperature that the vapor passing therethrough will not be condensed until it has effected the desired reaction upon the mineral coloring matter in the asbestos fibers. This heating of the containers may be effected by means of surrounding steam coils containing steam under presure, which will give a temperature considerably above 212 F, or where metallic containers are employed, the heat may be supplied by means of a gas flame or other direct heating means. The vapor containing the bleaching agent and watervapor passes to every portion of the asbestos fibers, instantly attacking the coloring matter and converting it into soluble salts. As before stated, the coloring matter consists principally of iron compounds (principally iron oxid) which are converted into soluble chlorids. After treatment of the fibers with the acid in thevapor stage, as before described, it is preferably dropped into a tank of water where the soluble chlorids, principally chlorids of iron, are removed by washing.

In some cases I may treat the fibers immediately after they are loosened up, and before any preliminary washing and drying thereof with the acid vapor, in which case the subsequent washing not.only removes the chlorid resulting fromthe acid vapor treatment, but also the dirt and other forne ieaie eign matter. Where the fibers are preliminarily washed and dried, before the bleaching, the dirt and foreign matter will have been removed before the acid vapor treatment, and the subsequent washing will effect the removal of the soluble chlorids, resulting from the acid vapor treatment.

After the fibers have been washed to free them from the soluble chlorids, they are dried in any desired manner, preferably by spreading them on a conveyer passing slowly through a steam heated container or drying room to eliminate the moisture from the fibers.

Tn carrying out my invention, it will be observed that an enormous saving in the amount of acid employed necessarily results, as a very small quantity of commercial hydrochloric acid can be converted into an enormous volume of vapor consisting of water vapor and hydrochloric acid gas, so that great economy is effected by my process. I also find that the vapor penetrates throughout the fibrous mass and, carries to every particle of it the hydrochloric acid gas in association with the water vapor, so that the iron compounds present are acted upon by the acid in a more concentrated form than is possible commercially where an aqueous solution of an acid is employed. It follows, therefore, that the bleaching of the fibers takes place in a very short time, a mere matter of minutes as compared with hours where bleaching solutions are used, and this enables the fibers to be rapidly passed through the bleaching operation and the bleaching and subsequent treatment of the asbestos fibers for manufacturing purposes, as spinning, weaving, etc., is thus greatly simplified and expedited. I have found that fibers of the South African brown asbestos and other discolored asbestos fibers when treated by my improved process can be used for all purposes for which high grade white asbestos is ordinarily employed, including the production of asbestos yarn or thread and the production of asbestos woven fabrics.

T do not desire to be limited to the use of hydrochloric acid as the bleaching agent, while that is my preferred bleaching agent by reason of its comparative cheapness and the fact that there is comparatively little danger in handling it. T may, however, employ in some cases a vapor consisting of water vapor and phosgen gas, for example, in the same manner as T have described the operation of my process in the foregoing specification. The use of phosgen gas is, however, somewhat objectionable on account of the poisonous efi'ects on the operatives, in case any material quantity of the What I claim and desire to secure by Letters Patent is r '1. The herein described process of bleaching asbestos, which consists in subjecting asbestos fibers to the action of an acid in a .gaseous condition in the presence of moisture, and then washing the fibers with water to remove the soluble salts so formed.

2. The herein described process of bleaching asbestos, which consists in subjecting asbestos fibers to the action of an acid in gaseous condition in conjunction with aqueous vapor, and then washing the fibers with water to remove the soluble salts so formed.

3. The herein described process of bleaching asbestos, which consists in subjecting the fibers of asbestos to the action of aqueous vapor associated'with hydrochloric acid gas, and then washing out the soluble chlorids so formed, with water.

l. The herein described process of bleaching asbestos fibers, which consists in treating the fibers in substantially dry condition in an inclo'sed chamber with hydrochloric acid in the form of vapor, and then washing the fibers with water to' remove the soluble chlorids.

5. The herein described process of bleaching asbestos fibers, which consists in treating the asbestos fibers with an acid in gaseous condition associated with water vapor, maintaining the fibers in loosely associated condition to facilitate the penetration of the gas and vapor to all parts thereof, and then washing the fibers with water to remove thesoluble salts so formed.

6. The herein described process of bleaching asbestos fibers, which consists in treating them with an acid in vaporous or gaseous form, and maintaining the fibers and'the gas or vapor at a sufiiciently high temperature 7 to prevent premature condensation thereof and to facilitate the penetration of the gas or vapor throughout the fibers, and then washing the fibers with water to remove the and maintaining the fibers in a loosely associated condition to facilitate the penetration of the gas and vapor to all particles thereof, and washing the fibers with water to remove thesoluble chlorids therefrom.

8. The herein described process of bleaching asbestos fibers, which consists in subj ecting the fibers in loosely associated condition to the action of an acid gas and aqueous vapor, agitating the fibers to maintain them in loosely associated relation, and applying heat to the fibers to prevent premature condensation of the gas or vapor, and then washing the fibers with water to remove the soluble salts so formed.

9. The herein described process of bleaching asbestos fibers, ,which consists in treating the fibers in loosely associated condition, to the action of hydrochloric acid, in the form of vapor, and applying heat to the fibers to prevent the premature condensation of said vapor and to facilitate its being brought into contact with all portions of the fibers, maintaining the fibers in said loosely associated condition, washing the fibers with water to dissolve the soluble chlorids so formed, and then drying the fibers.

In testimony whereof I afiix my signature.

CHESTER L. iir L. 

